1. Field of the Invention
The present invention relates to a speed change control device and a speed change control method for an automatic transmission for a vehicle, and, in particular, relates to a speed change control device and a speed change control method for an automatic transmission for a vehicle, which, during speed changing, suppress the time period until speed changing is completed becoming drawn out due to the accelerator being stepped down upon during torque down control, or the like.
2. Description of the Related Art
An automatic transmission for a vehicle which speed changes output rotation transmitted from a power source and outputs the resulting speed changed rotation may be employed in various types of vehicle. With this kind of automatic transmission it is per se known to perform so called torque down control, in which the output torque of the power source is temporarily reduced during the inertia phase of speed changing. For example, the speed change control device of the automatic transmission described in Japanese Laid-Open Patent Publication 2000-142182 is of this type. According to the technique disclosed in that document, by temporarily reducing the output torque of the power source based upon a torque down amount which corresponds to the input torque of the automatic transmission and the like during the inertia phase of speed changing, it is made possible to implement an appropriate speed change in a short time period, even if the engagement force of an engagement device which participates in the speed change is comparatively small.
Incidentally, in this prior art technique, during speed changing, return control is performed in which a return is executed from torque down control after the inertia phase period. Although, in this return control, taking the torque down amount at the start of return as a base, this torque down amount is gradually decreased to zero, if, during upshifting, this torque down control is performed according to the above described prior art technique during the inertia phase, then there is a risk that if, during the return control from this torque down control, the accelerator opening amount is increased due to stepping down upon the accelerator being performed or the like, then the actual torque down amount may become deficient as compared to the torque down amount which is required, and sometimes stagnation or retrogression of the speed change operation may be caused (which is a malfunction), so that the time period until speed changing is completed may become drawn out.